Design Guide Part 3 - North York Moors National Park

SECTION 3TREES3.7.4Demolition in Close Proximity to TreesIn some situations it may be necessary to undertake demolition work close to treesprior to protective fencing being erected. Careful planning and management (as setout in the Arboricultural Method Statement) is required to ensure that roots and thesoil structure are not damaged throughout this process. The following points shouldbe considered:• Access facilitation pruning should be carried out in accordance with aspecification prepared by an arboriculturalist.• Plant and machinery should operate from outside the RPA or fromtemporary ground protection designed to protect tree roots and soilstructure.• Demolition should work into the footprint of existing structures and wherehard surfaces are removed, this should be carried out carefully with handheld tools to avoid damage to any tree roots beneath.• If there are underground services within the RPA it may be more practical toseal these off to avoid excessive excavation.3.7.5Avoiding Tree Root Damage During ConstructionAny construction activity agreed within the RPA is likely to be confined to very limitedareas or to an agreed specification which does not damage roots. The main principlesfor construction within the RPA which will help ensure long term tree survival are asfollows:• If new surfaces are to be constructed, only loose organic material andvegetation should be removed – no surface skimming or general excavationshould take place.• If vegetation is to be killed prior to construction, specialist advice might berequired to determine the most suitable herbicide to use to avoid accidentaldamage to tree roots.• When ground levels are to be raised the fill material must not inhibit verticalgaseous diffusion. Suitable materials might include no-fines gravel, washedaggregate or cobbles. Builders’ sand should not be used because of its highsalt content which is toxic to tree roots.• Impermeable surfacing should be avoided because they restrict waterpenetration and gaseous diffusion.• In rare situations where the construction of foundations is proposed withinthe RPA, techniques such as pile and beam or suspended floors will only beagreed to where it has been clearly demonstrated that trees to be retainedwill not be adversely affected.For more complex proposals it will be necessary to employ a suitably qualifiedperson (engineer) to design a load suspension layer such as a cellular confinementsystem.58